Belt roller with damped force limiter

ABSTRACT

A self-locking belt roller has a housing and a belt winding shaft rotatably mounted in housing. A torsion rod has a first end connected in the belt winding shaft. A profile head is connected to a second end of the torsion rod. A blocking member, that is vehicle-sensitive and/or belt-sensitive, is mounted on the profile head and moveable into a locking position at the housing in which rotation of the belt winding shaft is blocked. An energy-dissipating structure is positioned within a force transmission path, including the profile head, the torsion rod, and the belt winding shaft, for increasing a restraining force before the torsion rod becomes effective or simultaneously to the torsion rod becoming effective and for obtaining a degressive force characteristic curve.

This application is a continuation of Ser. No. 08/945,305, filed Feb.13, 1998 and now U.S. Pat. No. 6,105,894, which was the National Stageof International Application No. PCT/SE96/00472, filed Apr. 11, 1996.

BACKGROUND OF THE INVENTION

The invention relates to a self-locking belt roller with avehicle-sensitive and/or seat belt-sensitive controllable blockingdevice, the belt roller being provided with a force limiting device forrestricted belt withdrawal when a blocking member is engaged, the forcelimiting device comprising a torsion rod which is connected on the onehand to the belt winding shaft and on the other hand to the blockingmember.

A belt roller having the above features is described in connection witha tightening device in DE 43 31 027 A1; however, the tightening deviceis not necessary for the function of the force limiting device in theknown belt roller. In the known belt roller, the force limiting deviceis constructed as a torsion rod, so that particularly when used inconnection with an airbag, the response of the force limiting deviceallows for an additional, but decelerated forward displacement of thebelted occupant. This is achieved in that, in the event of loading, asthe belt unwinds from the belt winding shaft the belt loading of thebelt winding shaft blocked by the blocking member is reduced by thetorsional rod which yields and allows for further rotation of the beltwinding shaft.

The disadvantage associated with the known belt roller is that theacting force is increased by the force limiting device as a result ofthe cold deformation of the material and the decreasing windingdiameter, i.e. as a result of the associated lever arm reduction; theassociated force-path characteristic curve is progressive. In thiscontext, further tests have shown that it is, for example, desirable fora higher restraining force to be exerted by the force limiting device atthe start of an accident, namely so long as the belted person is not incontact with the airbag, and only to allow a reduced restraining forceto be exerted via the belt roller once both safety devices areeffective.

It is therefore the object of the invention to use suitable measures tobetter adapt the force-path curve in a belt roller of the generic typeto the special features of the deceleration curve of the vehicle or ofthe vehicle occupants.

SUMMARY OF THE INVENTION

The idea upon which the invention is based is that, for connecting thetorsion rod to the blocking member, a profile head, which is connectedto the associated shaft end face and rotates together with the beltwinding shaft, is provided as a support for the radially deflectableblocking member, and in the force transmission path between the torsionrod, profile head and shaft an additional energy-dissipating structureis provided for increasing the restraining force prior to the torsionrod becoming effective and for obtaining a stepped and/or degressiveforce-path characteristic curve. The invention offers the advantagethat, prior to the force limiting device constructed as a torsion rodbecoming effective, the vehicle occupant still participates as a resultof the increased restraining forces in the relatively low initialdeceleration of the motor vehicle and later upon contact with the airbaga lower restraining force is exerted via the force limiting device. Inthis respect, it may be expedient to adjust the force-pathcharacteristic curve so that it decreases in step fashion or isgenerally degressive. Thus, the path of the chest acceleration or of theHIC index, for example, can be optimized by a degressive force-pathcharacteristic curve of the force limiting device as a function of thedeformation behavior of a torsion rod.

In accordance with a first embodiment of the invention, the additionalenergy-dissipating structure is arranged between the belt winding shaftand the profile head, so that a relative movement between the beltwinding shaft and the profile head is made possible by the uncoupling ofthe blocking member from the belt winding shaft. This relative movementcan be exploited for the arrangement of the energy-dissipatingstructure. In this respect, the energy-dissipating structure accordingto a first embodiment of the invention is formed by a connection betweenthe shaft end face and the profile head in the form of shearingjournals, so that the initial loading is absorbed by the shearingjournals and, after the destruction thereof, a reduced force level isadjusted as the torsion rod becomes effective. The arrangement can beadjusted in such a manner that the shearing journals shear off beforethe torsion rod becomes effective or overlap with the torsion rod.

Alternatively, projections may be provided on the profile head, whichengage in corresponding recesses arranged in the belt winding shaft anddeforming in the event of a movement of the belt winding shaft relativeto the profile head.

According to a further embodiment of the invention, theenergy-dissipating structure consists of a division of the torsion rodinto two torsion elements, which are arranged one within the other, areconnected in a positive-locking manner to one another, and are connectedas usual on the one hand to the belt winding shaft and on the other handto the profile head; the different design of the two torsion elements isselected in such a manner that one of the torsion elements fails at anearlier point in time than the other so that, after the failure of thefirst torsion element, only the second torsion element is effective.

According to embodiments of the invention, the torsion elements can bemade of materials of different ductility, the inner torsion rodpreferably being made of a less ductile material. Alternatively, thetorsion elements can have different torsion lengths, the “torsionlength” being the length of the smallest cross section of the torsionrod.

According to a further embodiment of the invention, in order to adjustan energy-dissipating structure, the torsion rod is constructed as apolygonal tube, whose profile constricts as it absorbs force, so thatthe polar moment of resistance and therefore carrying capacity of thetorsion rod decreases.

In a further development of the invention, the torsion rod can beconstructed as a rectangular element having a casing which surrounds therectangular element and is made of a suitable plastics material. Thisdesign offers the advantage that the torsion rod can now be manufacturedas a punched part, rather than as the usual turned part in the state ofthe art, the fitted plastics material casing forming an additionalmoment of resistance when the torsion rod is twisted, until the casingis blown off as a result of the changing shape within the casing as thetorsion rod is twisted. In this context, it is expedient for therectangular tube to comprise corresponding connection elements having arectangular cross section at its two ends for the connection of theprofile head and the belt winding shaft, and for the casing to extendbetween the connection elements.

According to an embodiment of the invention, it can be provided that theinner receiving aperture of the belt winding shaft corresponds in itscross section to the dimension of the casing of the torsion rod whichcan be pushed into the receiving aperture. This results in the followingadvantage: As the torsion rod is twisted, the plastics material casingfitted over the torsion rod is plastically deformed after being blownoff the torsion rod, since the casing cannot escape in the receivingaperture of the belt winding shaft in which it is enclosed.

However, it is also provided in an embodiment of the invention that thetorsion rod is constructed as a turned part having a round cross sectionand is provided with a casing made of a suitable plastics material whichis fitted over the torsion rod, the moment of resistance in thisembodiment essentially being generated by the friction or cohesionbetween the torsion rod and the casing.

Finally, it can be provided according to an embodiment of the inventionthat the belt winding shaft engages around the profile head with arecess and a bending bolt, which deforms when the belt winding shaftmoves relative to the profile head, is arranged between the profile headand the belt winding shaft. In this respect, according to an embodimentof the invention, the profile head can comprise a flattened area over acircumferential section and the bending bolt, which is held at both endsagainst the belt winding shaft, can be arranged resting upon theflattened area in the recess of the belt winding shaft in its extendedstate. When a corresponding torque acts upon the belt winding shaft, thelatter rotates relative to the profile head, which is held by theblocking member, the deformation of the bending bolt occurring over alarge angular range, resulting in a longer period of energy dissipation,the torsion rod subsequently or simultaneously becoming effective as aforce limiting device.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are described in further detail below andare illustrated in the drawings, in which:

FIG. 1 is a schematic view of a belt roller,

FIG. 2 is a schematic view of a shaft with torsion rod,

FIG. 3 is a detailed view of a torsion rod according to the invention,

FIG. 4 shows a torsion rod constructed as a rectangular element withcasing,

FIG. 5 shows the torsion rod according to FIG. 4 without casing,

FIG. 6 is a cross section through the subject matter of FIG. 4,

FIG. 7 is a schematic view of the belt winding shaft of the belt rollerhaving a torsion rod according to FIG. 4, and

FIG. 8 is a sectional view of the connection between the belt windingshaft and the profile head.

DESCRIPTION OF PREFERRED EMBODIMENTS

As firstly shown in FIG. 1, the belt roller comprises a U-shaped housing10, in whose U-limbs 11 or the apertures 12 arranged therein a beltwinding shaft 13 is mounted. At the blocking end of the belt windingshaft 13, a profile head 14, which rotates within the U-limb 11 of thehousing 10, is associated with the end face of the belt winding shaft13. Mounted on the profile head 14 is a blocking member 15, which can beradially deflected under the action of a control device, not shown, andwhich is controlled so as to be guided into the toothing 25 arranged inthe associated aperture 12 in the event of deceleration.

The profile head 14 and the belt winding shaft 13 are connected to oneanother by a torsion rod 16 acting as a force-limiting device, theconnection being formed in that one end of the torsion rod 16 isconnected preferably in a positive-locking manner to the profile head14, and the other end of the torsion rod 16 extending in the beltwinding shaft 13 is connected to the belt winding shaft 13 in a mannernot shown. If, after the blocking of the profile head 14 by means of theblocking member 15, there is a further belt extraction with acorresponding rotation of the belt winding shaft 13, then thisrotational movement is transmitted via the torsion rod 16 with asimultaneous absorption of energy to the profile head 14, either anabutment being provided between the belt winding shaft 13 and theprofile head 14 to limit the deformation of the torsion rod 16 or thetorsion rod being constructed in such a manner that it can carry out alarger number of rotations than is required for the energy conversion.In order to provide an additional, energy-dissipating structure in theforce transmission path, at least one shearing element 25 is provided atthe end face of the belt winding shaft 13 facing the profile head 14,which shearing element engages in an associated bore 26 in the profilehead 14. By means of the cross sectional surface area of the shearingelement and its distance from the pivot axis of the belt winding shaft13 or profile head 14, it is possible to adjust a torque and path insuch a manner that the shearing element shears off and thus the soleloading of the torsion rod 16 is effected. After the shearing off of theshearing element, the torque is exclusively transmitted by the torsionrod 16.

FIG. 2 illustrates an alternative embodiment, in which one or moreprojections 27 manufactured from a harder material are fitted in theprofile head 14, the projections 27 engaging in recesses located on theassociated end face of the belt winding shaft 13; these recesses aredeformable, so that there is a corresponding energy dissipation from thestart of loading.

FIG. 3 illustrates a further embodiment of the invention, in which thetorsion rod 16 comprises an outer torsion element 17 and an innertorsion element 18 extending within the outer torsion element; the innertorsion element is manufactured from a less ductile material and/or hasa shorter “torsion length”, which is the length which applies to thesmallest cross section of the torsion rod. As a result of this design,the inner torsion element fails before the outer torsion element and thefurther acting torque is then only transmitted by the outer torsionelement 17. Corresponding force-path curves can be adjusted by theselection of material, diameter and torsion length of the inner torsionelement 18.

A further alternative, not illustrated in the drawings, consists inconstructing the torsion rod 16 as a polygonal tube—cf, for example,FIG. 3, position 17—, the profile constricting and the polar moment ofresistance and therefore the carrying capacity of the torsion rod 16decreasing during the plastic torsion of the torsion rod 16. In thismanner, it is possible to adjust a corresponding force-pathcharacteristic curve which is degressive from the start.

In accordance with the embodiment illustrated in FIGS. 4 to 7, thetorsion rod is formed by a rectangular element 35, which is providedwith an enclosing casing 32 made of a suitable plastics material. Inthis case the rectangular element 35 comprises at each of its two outerends a connection element 33 having a rectangular cross section for theconnection of the profile head 14 or belt winding shaft 13,respectively, the casing 32 extending between these connection elements33. As shown in detail in FIG. 6, the edges 34 of the rectangularelement 35 are rounded with a radius, so that a good connection betweenthe rectangular element 35 and the casing 32 is provided.

If the embodiment of the torsion rod illustrated in FIGS. 4 to 6 isloaded in an assembly according to FIG. 1, then the positive lockingbetween the rectangular element 35 and the plastics material casing 32results in an increased moment of resistance, until the casing 32 isblown off by the changing form of the rectangular element 35. As shownin FIG. 7, this moment of resistance can be increased when the receivingaperture 29 located in the belt winding shaft 13 corresponds in itscross section to the dimension of the casing 32 of the torsion rod 16which is to be pushed into the receiving aperture 29, which means thatthe plastics material casing cannot escape when it is blown off by thetwisting of the rectangular element 35, but is plastically deformed.This means that a slower decline in the force-path curve can beadjusted. In this respect, the course of the force-path curve is morespecifically also dependent upon the type of plastics material used, asofter plastics material resulting in a softer curve and a harderplastics material in a steeper curve during the rise and fallrespectively of the force path.

Finally, FIG. 8 shows an embodiment in which the energy-dissipatingstructure is arranged between the belt winding shaft 13 and the profilehead 14 in that the belt winding shaft 13 encloses the profile head 14with a recess 21. In this case, the profile head 14 comprises aflattened area 20 over a circumferential section, the recess 21 of thebelt winding shaft 13 rising above the flattened area 20 with anadditional clearance 24. In its extended position, a bending bolt 19 isarranged so as to rest upon the flattened area 20 of the profile head14. The bending bolt 19 is secured at one end with a positive-lockingconnection 22 to the belt winding shaft 13, whilst the other end of thebending bolt 19 arranged in its extended position lies in a recess 23 inthe belt winding shaft 13. When this connection is correspondinglyloaded, as a result of the rotation of the belt winding shaft 13relative to the profile head 14 which is held by the blocking member 15,the bending bolt 19 is deformed over the angular range provided by theflattened area in that the bending bolt is pressed into the contour ofthe clearance 24 of the recess 21, the associated end of the bendingbolt finding the required escape space in the recess 23. After acorresponding deformation of the bending bolt 19, the level of forceacting upon the torsion rod is reduced.

The features of the subject matter of this document disclosed in theabove description, the patent claims, the abstract and the drawings canform the basis, either individually or in any combination, for therealization of the invention in its different embodiments.

What is claimed is:
 1. A self-locking belt roller comprising: a housing:a belt winding shaft rotatably mounted in said housing; a torsion rodhaving a first end connected in said belt winding shaft; a profile headconnected to a second end of said torsion rod; a blocking member, thatis vehicle-sensitive or belt-sensitive or vehicle- and belt-sensitive,mounted on said profile head and moveable into a locking position atsaid housing in which rotation of said belt winding shaft is blocked; anenergy-dissipating structure positioned within a force transmissionpath, including said profile head, said torsion rod, and said beltwinding shaft, for increasing a restraining force simultaneously to saidtorsion rod becoming effective and for obtaining a degressive forcecharacteristic curve.
 2. A belt roller according to claim 1, whereinsaid energy dissipating structure is connected to said belt windingshaft and said profile head.
 3. A belt roller according to claim 2,wherein said energy dissipating structure comprises at least oneshearing journal connected to said belt winding shaft and wherein saidprofile head has at least one bore in which said at least one shearingjournal is positioned.
 4. A belt roller according to claim 2, whereinsaid energy dissipating structure comprises at least one projectionconnected to said profile head and wherein said belt winding shaft hasat least one recess in which said at least one projection is positioned,wherein said at least one recess deforms when said belt winding shaftrotates relative to said profile head.
 5. A belt roller according toclaim 1, wherein said torsion rod comprises a first and a second torsionelements, wherein said first torsion element is positive-lockinglymounted inside said second torsion element.
 6. A belt roller accordingto claim 5, wherein said first and second torsion elements are made ofmaterials of different ductility.
 7. A belt roller according to claim 5,wherein said first torsion element has a different length than saidsecond torsion element.
 8. A belt roller according to claim 1, whereinsaid torsion rod is a tube of polygonal cross-section.
 9. A belt rolleraccording to claim 1, wherein said torsion rod is comprised of arectangular element and a plastic casing surrounding said rectangularelement.
 10. A belt roller according to claim 9, wherein: saidrectangular element has a first end with a first connection element anda second end with a second connection element; said casing extends fromsaid first connection element to said second connection element; aidfirst and second connection elements have a rectangular cross-section;said first connection element connects said rectangular element to saidprofile head; and said second connection element connects saidrectangular element to said belt winding shaft.
 11. A belt rolleraccording to claim 10, wherein said belt winding shaft has a receivingaperture having a cross-section matching a cross-section of said casing,wherein said casing is received in said receiving aperture.
 12. A beltroller according to claim 1, wherein said torsion rod is comprised of aturned part having a round cross-section and a casing enclosing saidturned part.
 13. A belt roller according to claim 1, wherein said beltwinding shaft has a recess in which said profile head is received,wherein said energy-dissipating structure is a bending bolt that restsat said profile head and engages said recess, wherein aid bending boltdeforms when said belt winding shaft moves relative to said profilehead.
 14. A belt roller according to claim 13, wherein said profile headhas a flattened area over a circumferential portion thereof and whereinsaid bending bolt has two ends engaging said recess of said belt windingshaft and rests in a rest position thereof at said flattened area ofsaid profile head.